Hydroformylation reactions involve the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (i.e., syn or synthesis gas) with carbon compounds containing olefinic unsaturation. The reaction is performed in the presence of a carbonylation catalyst and results in the formation of a compound, for example an aldehyde, which has one more carbon atom in its molecular structure than the starting olefinic feedstock. By way of example, higher alcohols may be produced in the so-called "oxo" process by hydroformylation of commercial C.sub.6 -C.sub.12 olefin fractions to an aldehyde-containing oxonation product, which on hydrogenation yields respective C.sub.7 -C.sub.13 saturated alcohols. The crude product of the hydroformylation reaction will contain catalyst, aldehydes, alcohols, unreacted olefin feed, syn gas and by-products.
Before further processing of the crude product is possible, it is necessary to remove the catalyst therefrom. One conventional method of removing cobalt values from such a crude product is to treat the product with an alkali or acid wash technique. See U.S. Pat. No. 3,725,534 (Reisch), which issued on Apr. 3, 1973. However, this approach uses expensive raw materials and incurs problems associated with finally removing essentially all traces of cobalt from the water wash streams before being discharged.
Another conventional method involves the oxidation of the cobalt catalytic species followed by extraction as a salt in aqueous solution. See U.S. Pat. No. 2,744,921 (Mertzweiller et al.), which issued on May 8, 1956.
U.S. Pat. No. 4,625,067 (Hanin), which issued on Nov. 25, 1986, discloses what is commonly referred to as the "Cobalt Flash" method. Cobalt Flash involves the contacting of the crude product with a stream of stripping gas to entrain volatile cobalt compounds. The contacting is performed in the presence of water and aqueous acid to dissolve those cobalt values not entrained in the gas under the conditions of temperature and pressure employed for the contacting, and the aqueous phase is subsequently separated from the organic hydroformylation reaction product.
U.S. Pat. No. 3,868,422, which issued on Feb. 25, 1975, and Great Britain Patent No. 893,524, which issued in 1962, are also directed to cobalt catalyst removal cycles which involve the stripping of volatile hydridocobalt carbonyl from crude oxo reaction products.
The goal of any stripper-reactor is two-fold. First, it must remove as much cobalt as possible from the oxo product, and second, it must maximize the percent of volatile cobalt recovered overhead. The first goal is important for meeting product quality specifications, maximizing the hydrogenation catalyst life, and avoiding cobalt losses. The second is important for improved oxo reactor performance and for minimizing the amount aqueous cobalt salts which must be recycled to oxo.
The present invention is an improvement over known stripping devices. Typical strippers recycle the reflux product to the top portion of the stripper, thereby forming what the present inventors have discovered is a single zone reactor chamber wherein the entire stripper functions as both a stripper and reactor.
The present inventors have developed, through extensive comparative experimentation, a stripper-reactor which is capable of carrying out the Cobalt Flash stripping process more efficiently, i.e., volatile cobalt recovery is substantially increased. This novel stripper-reactor increases volatile cobalt recovery by approximately 5-10% over conventional stripper which recycle reflux to the top portion of the stripper. Cobalt recovery is substantially increased by the formation of distinct stripper and reaction zones within the stripper-reactor. The present inventors have discovered, as demonstrated in the comparative examples below, that the location of the reflux recycle within the stripper-reactor is extremely critical in improving the recovery of volatile cobalt during the cobalt Flash process. Moreover, it was highly unexpected that the location of the reflux recycle on the stripper-reactor would provide such a marked increase in volatile cobalt recovery. It is believed that volatile cobalt recovery is greatly enhanced because volatile cobalt in the pure stripping zone is rapidly removed before it decomposes to nonvolatile Co.sub.2 (CO).sub.8 which can cause a decrease in overhead cobalt recovery.
To the contrary, conventional stripping devices typically recycle reflux product to the top of the reactor thereby forming a single combined stripping and reaction zone within the reactor chamber. This single zone allows for the undesirable decomposition of HCo(CO).sub.4 to Co.sub.2 (CO).sub.8 which decreases the overhead volatile cobalt recovery. This is primarily due to the longer retention time of volatile cobalt within the stripper-reactor.
The present inventors have also discovered that the water and organic acid feed port location about the Cobalt Flash system can slightly increase overhead volatile cobalt recovery as well.
The present invention also provides many additional advantages which shall become apparent as described below.